Decomposition of the refuse within a sanitary landfill produces landfill gas which contains methane and impurities. For example, the impurities may include carbon dioxide, water and various hydrocarbons.
Although the concentration of methane in landfill gas varies, methane may comprise about 50 percent by volume of the landfill gas. In some instances, the landfill gas is used without removal of the impurities, and in other instances, the concentration of the methane is increased by removing some, or substantially all, of the impurities.
Impurities can advantageously be removed in an adsorption process, and one such process is disclosed in Bingham U.S. Pat. No. 4,000,990. In the Bingham process, landfill gas is first passed through a pretreating adsorption zone where the water in th gas is adsorbed. Subsequently, the landfill gas is passed through an additional adsorption zone to remove substantially all of the other impurities. After the adsorbent material in the pretreating zone becomes saturated with impurity, the saturated zone is thermally regenerated by passing a hot regeneration gas through it. This removes the impurity from the pretreating adsorption zone and makes it ready for subsequent use on stream.
The process described in the Bingham patent works very well to provide product fluid having an extremely high concentration of methane. However, corrosion problems developed in the pretreating adsorption zones and in the thermal regeneration system for the pretreating adsorption zones. Although the existence of the corrosion was self-evident, the cause of the corrosion was not apparent and was difficult to ascertain.